here`s a good tip to clear the room.
hire one random hero.
from the streetpass heroes, hire one hero with a light blue top, and two mii`s with any colour as long as they are both the same colour. with these two mii`s, if you can, try to find one that is at least level 3 or higher (preferably both of them really).
when you enter the room, the random hero will get scared and run away. use the light blue top hero to freeze a mummy. then use the team up option for the remaining two heroes.
with two mii`s teamed up, they combine their power plus one level, and you`ll get an extra hit too. and while the mummy is frozen, you can get an extra hit in, maybe even a few depending how quick the mummy shrugs ofv the ice.

That level is extremely easy for me. Just re recruit level 7 Red shirt heroes and after a while one of them won't flee. Then use fire and half of their life bars will go down!

Hire at least two Wanderers to lead the party, then whoever the hell you actually want to use. That works for me, and means that if the two in front get scared off, the Mummies won't scare off the other guys. If you're still having trouble, hire two weak Wanderers, one Light Green/Light Blue Wanderer/Hero, Two Green Wanderers or Heroes, one other random guy and ideally someone with the same colour shirt as the random guy. Two wanderers scared off, Mummies frozen/put to sleep, two Green Miis team up and use magic, next guy immediately level 7 if not already, maybe teams up to become something like level 10 or level 14 and wipes out the enemies in one or two hits.